Sealed Rotary Shaft Force Sensor for Contamination-Free Robot Joints

Solution Overview

Problem

Conventional rotary shaft structures in collaborative robots face issues with foreign matter ingress leading to force sensor corrosion and failure, and umbilical members breaking due to rotational movement, which affect detection accuracy.

Innovation Solution

A rotary shaft structure with a flexible deformation body sealing the force sensor and reducing umbilical members, using a communication substrate for serial or wireless communication, and a failover detection circuit to stabilize detection accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the force sensor is sealed with a cover, packing or bolts to prevent foreign matter ingress, then reliability is improved, but the outer diameter and thickness increase making the rotary shaft structure larger and heavier

Engineering Contradiction:

Improveforce sensor protection from foreign matterVSAvoidrotary shaft structure weight

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The patent extracts the sealing function from a separate cover structure and integrates it into the driven body itself. The driven body is designed with a sealed structure that directly houses the force sensor, eliminating the need for additional cover, packing, and bolt components. This integration maintains foreign matter protection while significantly reducing the overall size and weight of the rotary shaft structure.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If the force sensor is sealed with a cover, packing or bolts to prevent foreign matter ingress, then reliability is improved, but the outer diameter and thickness increase making the rotary shaft structure larger

Engineering Contradiction:

Improveforce sensor protection from foreign matterVSAvoidrotary shaft structure length

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The patent extracts the sealing function from a separate cover structure and integrates it into the driven body itself. The driven body is designed with a sealed structure that directly houses the force sensor, eliminating the need for additional cover, packing, and bolt components. This integration maintains foreign matter protection while significantly reducing the overall size and weight of the rotary shaft structure.

Inventive Principle:

Principle #2Taking out (Extraction)

3Ease of operation

If umbilical members are arranged inside the robot mechanism, then ease of operation is improved, but the members may break or become broken due to rotational movement of the joint

Engineering Contradiction:

Improveumbilical member safetyVSAvoidumbilical member durability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent applies dynamic design principles to the umbilical member arrangement. The umbilical members are routed to allow for the rotational movement of the joint, with sufficient clearance and flexibility built into the routing path. This dynamic arrangement accommodates the joint's rotation without creating excessive tension or friction that would lead to breakage, while keeping the members inside the robot mechanism for safety.

Inventive Principle:

Principle #15Dynamics

4Reliability

If umbilical members are not constrained to allow free movement, then reliability is improved, but forces for restoring the umbilical member to its original state are exerted on the force sensor reducing detection accuracy

Engineering Contradiction:

Improveforce sensor functionalityVSAvoidforce sensor detection accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent introduces an intermediary element in the form of a guide structure or routing mechanism that directs the umbilical members along a predetermined path. This intermediary arrangement allows the members to move freely during joint rotation without exerting restoring forces on the force sensor, as the guide structure supports the members' movement without creating friction or tension that would affect sensor accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Prevents foreign matter ingress and umbilical member damage, allowing for a smaller, lighter, and more accurate force sensor detection without reaction forces.

Implementation Method 1

a flexible deformation body which is in contact with the output shaft and the driven body, wherein the entirety of the force sensor is sealed by the output shaft, the driven body, and the flexible deformation body

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS12496731B2Rotating shaft structure provided with force sensor, and robot

Publication Date: 2025.12.16 FANUC LTD

AI summary

A rotary shaft structure includes an actuator having an output shaft for rotationally driving a driven body, a force sensor which is arranged between the output shaft and the driven body and which detects a force exerted between the output shaft and the driven body, and a flexible deformation body which is in contact with the output shaft and the driven body, wherein the entirety of the force sensor is sealed by the output shaft, the driven body, and the flexible deformation body.